The present invention relates to waveguide antennae, and more particularly to circularly polarized waveguide antennae.
FIG. 9 illustrates a first conventionally known circularly polarized antenna array 900. In this configuration, the circularly polarized antenna array employs two linearly-polarized antenna elements 912 and 914 with 90 degree phase difference, the 90 degree phase difference usually provided by a hybrid coupler 920. Multiple instances of the antenna waveguide elements 912/914 and accompanying hybrid coupler 920 are implemented to complete construction of the array, and a power divider 930 is used to supply each of the hybrid couplers 920 forming the array 900.
FIG. 10 illustrates a second conventionally known circularly polarized waveguide slot array 1000. Each array element 1010 consists of a circularly polarized waveguide antenna and septum polarizer, an example of which is disclosed in the commonly-owned U.S. Pat. No. 6,118,412. A power divider 1020 is used to feed each of the array elements 1010.
In each of the conventional implementations of FIGS. 9 and 10, the spacing between the array elements (e.g., between a first instance of elements 912/914 and a second instance of elements 912/914 in FIG. 9) must not be excessively large, otherwise grating lobes will appear. For example, if the spacing between neighboring array elements is greater than λg/2, grating lobes will appear (λg represents the guide wavelength of a signal intended to propagate within the waveguide). However at the expected frequency of operation, the separation λg/2 is quite small, and keeping the spacing of contiguous array elements within this distance is difficult to realize.
What is needed is a new design for a circularly polarized waveguide slot array which will overcome the aforementioned difficulties.